Add Qt Gradle Plugin platform config

We want automated testing for QtGP. Test cases that can be run with
Gradle have been made a while ago, but they were only run locally by the
developers.

This commit adds Linux/macOS/Windows configurations for QtGP. These are
marked TestOnly as the build/test process in Gradle is packaged together
and we don't want to initiate builds for the Qt side.

Task-number: QTTA-217
Change-Id: I777d191596f43089d0ad80cbb6470c62a0eee257
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

coin/platform_configs/qtgradleplugin.yaml

@@ -0,0 +1,18 @@
+Version: 2
+Include: []
+Configurations:
+-
+    Id: 'qtgp-on-linux'
+    Template: 'qtci-linux-RHEL-9.4-x86_64-50'
+    Compiler: 'GCC'
+    Features: ['TestOnly']
+-
+    Id: 'qtgp-on-macos'
+    Template: 'qtci-macos-14-arm-106'
+    Compiler: 'Clang'
+    Features: ['TestOnly']
+-
+    Id: 'qtgp-on-windows'
+    Template: 'qtci-windows-11_23H2-x86_64-53'
+    Compiler: 'MSVC2022'
+    Features: ['TestOnly']